The distribution of Aspergillus spp. opportunistic parasites in hives and their pathogenicity to honey bees

Kirsten Foley,Géraldine Fazio,Annette B Jensen,William O.H Hughes

doi:10.1016/j.vetmic.2013.11.029

Kirsten Foley, Géraldine Fazio + Show 2 more

Open Access

https://doi.org/10.1016/j.vetmic.2013.11.029

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Abstract

Stonebrood is a disease of honey bee larvae caused by fungi from the genus Aspergillus. As very few studies have focused on the epidemiological aspects of stonebrood and diseased brood may be rapidly discarded by worker bees, it is possible that a high number of cases go undetected. Aspergillus spp. fungi are ubiquitous and associated with disease in many insects, plants, animals and man. They are regarded as opportunistic pathogens that require immunocompromised hosts to establish infection. Microbiological studies have shown high prevalences of Aspergillus spp. in apiaries which occur saprophytically on hive substrates. However, the specific conditions required for pathogenicity to develop remain unknown. In this study, an apiary was screened to determine the prevalence and diversity of Aspergillus spp. fungi. A series of dose–response tests were then conducted using laboratory reared larvae to determine the pathogenicity and virulence of frequently occurring isolates. The susceptibility of adult worker bees to Aspergillus flavus was also tested. Three isolates (A. flavus, Aspergillus nomius and Aspergillus phoenicis) of the ten species identified were pathogenic to honey bee larvae. Moreover, adult honey bees were also confirmed to be highly susceptible to A. flavus infection when they ingested conidia. Neither of the two Aspergillus fumigatus strains used in dose–response tests induced mortality in larvae and were the least pathogenic of the isolates tested. These results confirm the ubiquity of Aspergillus spp. in the apiary environment and highlight their potential to infect both larvae and adult bees.

Highlights

The increasing demand upon honey bees for pollination services and their recent unexplained colony losses has lead to a surge of public and scientific interest in honey bee Apis mellifera pathology (Evans and Schwarz, 2011; Aizen and Harder, 2009)
Three isolates (A. flavus, Aspergillus nomius and Aspergillus phoenicis) of the ten species identified were pathogenic to honey bee larvae
Adult honey bees were confirmed to be highly susceptible to A. flavus infection when they ingested conidia

Summary

Introduction

The increasing demand upon honey bees for pollination services and their recent unexplained colony losses has lead to a surge of public and scientific interest in honey bee Apis mellifera pathology (Evans and Schwarz, 2011; Aizen and Harder, 2009). Honey bees are faced with multiple stressors such as poor nutrition, pesticides and exposure to pathogens, which combined may have a significant impact on colony survival (van Engelsdorp and Meixner, 2010). Honey bees are susceptible to high diversity of parasites of which certain newly emerged groups e.g. viruses, Varroa destructor, Nosema ceranae (Amdam et al, 2004; Fries, 2010; Genersch and Aubert, 2010) have attracted much attention. The impacts of other less studied parasites on colony health as well as their interactions with other stressors may deserve more consideration. Stonebrood is considered to be a pathogen of low virulence in honey bee colonies yet very little is known regarding the stonebrood and honey bee host–parasite system (Gilliam and Vandenberg, 1988; Bailey, 1968). A number of species from the genus Aspergillus are facultative parasites and have been reported as agents of

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